Dalmatian Toadflax: Wicked Weed Of The West

It used to be common in gardens as a pretty ornamental plant. Now it's common on rangeland. It's still pretty, but it's choking out good pasture grasses.With yellow flowers and heart-shaped leaves, Dalmatian toadflax is a noxious weed that grows up to 4 ft. tall. Its specialty is invading pastureland where plant health is poor, says University of Idaho weed scientist Don Morishita."It can be a fairly

Jenny Bushnell | Sep 01, 1998

It used to be common in gardens as a pretty ornamental plant. Now it's common on rangeland. It's still pretty, but it's choking out good pasture grasses.

With yellow flowers and heart-shaped leaves, Dalmatian toadflax is a noxious weed that grows up to 4 ft. tall. Its specialty is invading pastureland where plant health is poor, says University of Idaho weed scientist Don Morishita.

"It can be a fairly competitive plant, especially if the condition or the health of an area isn't very good," Morishita says.

Dalmatian toadflax extends throughout the western U.S., from Colorado to Washington and California. It has also been found in eastern states, including New York, Pennsylvania, Connecticut and Maine, though it hasn't yet posed much of a threat there. It's also showing up in the Great Lakes area, including Wisconsin and Michigan.

The weed isn't toxic to cattle, but it prevents other, more nutritious, plants from growing. Morishita says it spreads by seed and also through a far-reaching root system.

Dalmatian toadflax is common in roadside ditches, rocky hillsides and anywhere plant life has been disturbed.

Manage For Prevention The best way to prevent it from getting a grip on your land is to manage pastureland well, Morishita says. It's especially important to not overgraze an area or let plant health become weak.

Morishita also says to be aware of the problem. Because of the pretty yellow flower, people sometimes pick the weed and then discard it a few miles down the road, inadvertently spreading it to a new area.

Above all, prevent the weed from producing seed, says University of Wyoming Extension weed scientist Tom Whitson. "Keeping it from going to seed is critical," he says.

If plant health is already poor, give field grasses full opportunity to compete with the weed, Whitson adds. "We need to delay grazing until the grasses have come to full seed head," he says. "We need to maximize perennial cool-season grass competition. When we have noxious weeds on rangeland, we've got to nurture those perennial grasses back to health."

Eradication Methods Controlling Dalmatian toadflax is a long process. Whitson says getting rid of individual weeds helps. If you see Dalmatian toadflax on rangeland, "get off the horse and pull that weed," he says.

If you have a large area where Dalmatian toadflax has set in, it's sometimes better to contain the weed than to spend lots of time and money to eradicate it. University of Idaho's Morishita says to apply herbicides around the edges of the patch to keep the infestation under control.

For eradicating the weed instead of containing it, Morishita says cultivation works. "It's fairly susceptible to cultivation, but in rangeland that's not always a practical form of control," he says.

If cultivation isn't possible, herbicides like picloram are fairly effective at destroying the weed. "For most of our rangeland, herbicides tend to be the most frequently used and easiest form of control, though not always the least expensive or most effective," Morishita says.

He cautions that herbicides won't be effective during a drought or if the weed isn't healthy. "If the plant is not growing well, it's not going to take up that chemical," he says.

Herbicides are most effective if applied about two weeks after the first killing frost, Whitson says, because the plant is more vulnerable at that time. "The waxy cuticle is broken by the first frost," he says.

Whitson also suggests a two-pronged attack on the weed. "The use of a herbicide along with the introduction of a cool-season perennial grass has been effective," he says. Grasses such as crested wheatgrass, pubescent wheatgrass and smooth bromegrass provide good competition for Dalmatian toadflax. This method only works, however, if the grasses are allowed to come to full seed head before cattle begin grazing. The process takes two to three months.

But don't re-seed if the grasses already in the field could compete with the weed if they had the chance, says Montana State University weed scientist Roger Sheley.

He also recommends adding deep-rooted plants, like alfalfa, that can compete with Dalmatian toadflax's deep roots. "Put in an alfalfa-grass mix to compete with deep tap-rooted weeds," Sheley says.

A Similar Weed Yellow toadflax is a relative of Dalmatian toadflax. It has similar yellow flowers, though its leaves are long and thin. It acts much like Dalmatian toadflax, infesting the same areas and spreading in the same way. Though more common in Eastern states than in the West, it is found throughout the country. Treat yellow toadflax the same way you would treat Dalmatian toadflax, says University of Idaho's Morishita.

To order Montana State University's Dalmatian and Yellow toadflax bulletin, write to Extension Publications, P.O. Box 172040, Bozeman, MT 59717-2040, or call 406/994-3273. For out of state orders, enclose $1.